<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }
        
        .wrap {
            width: 300px;
            margin: 100px auto 0;
        }
        
        table {
            border-collapse: collapse;
            border-spacing: 0;
            border: 1px solid #c0c0c0;
            width: 300px;
        }
        
        th,
        td {
            border: 1px solid #d0d0d0;
            color: #404060;
            padding: 10px;
        }
        
        th {
            background-color: #09c;
            font: bold 16px "微软雅黑";
            color: #fff;
        }
        
        td {
            font: 14px "微软雅黑";
        }
        
        tbody tr {
            background-color: #f0f0f0;
        }
        
        tbody tr:hover {
            /* cursor: pointer; */
            background-color: #fafafa;
        }
    </style>

</head>
<body>
    <div class="wrap">
    <table>
        <thead>
            <tr>
                <th>
                    <input type="checkbox" id="j_cbAll" />
                </th>
                <th>商品</th>
                <th>价钱</th>
            </tr>
        </thead>
        <tbody id="j_tb">
            <tr>
                <td>
                    <input type="checkbox" />
                </td>
                <td>iPhone8</td>
                <td>8000</td>
            </tr>
            <tr>
                <td>
                    <input type="checkbox" />
                </td>
                <td>iPad Pro</td>
                <td>5000</td>
            </tr>
            <tr>
                <td>
                    <input type="checkbox" />
                </td>
                <td>iPad Air</td>
                <td>2000</td>
            </tr>
            <tr>
                <td>
                    <input type="checkbox" />
                </td>
                <td>Apple Watch</td>
                <td>2000</td>
            </tr>

        </tbody>
    </table>
    </div>
    <script>
        var all = document.getElementById('j_cbAll');
        var inputs = document.querySelector('#j_tb').getElementsByTagName('input');
        all.onclick = function() {
            // 获取选框的状态，选中为ture，
            //console.log(all.checked);
            for(var i = 0; i < inputs.length; i++) {
                inputs[i].checked = this.checked;
            }
        }
        for(var j = 0; j < inputs.length; j++) {
            inputs[j].onclick = function() {
                flag = true;
                // 检查选框有没有都选
                for(var t = 0; t < inputs.length; t++) {
                    console.log(inputs[t].checked);
                    if (inputs[t].checked == false) {
                        flag = false;
                        break;
                    }
                }
                all.checked = flag;
        }
        }
    </script>
</body>
</html>